1. Field of the invention
This invention relates to watertight wrist-watch casings particularly of the type including a caseband and an independent bottom removably secured to said caseband by means of screws crossing the bottom and causing a thin gasket of elastomeric material to be compressed between the caseband and the bottom so as to form a tight seal between these two pieces.
2. Description of the prior art
With the casings of that type, which are known in the art, the gasket is an independent piece which accordingly must be set in place separately (US - A - 4 015 422).
The thinner the gasket is chosen, the more supple it must be in order to provide the proper seal. Now, setting a very supple gasket in place is not an easy task. If the gasket has been laid on the bottom of its lodging for instance of the caseband, setting the bottom in place may easily shift the gasket aside or fold it or even crumple it, thus jeopardizing the casing tightness, because once the casing is closed, the condition of the gasket can no longer be checked. Moreover, in manufacturing the gasket and the metallic casing pieces separately, the gasket will hardly fit the lodging provided for it in the metallic casing pieces in the proper manner, because of the tolerances, if the metallic casing pieces butt against each other in closed condition. Otherwise, if the bottom is pressed against the gasket without abutting against the caseband, there is a great risk of exceeding the limit of elasticity of the gasket upon securing the bottom to the caseband. Anyway, with an independent gasket a lodging for it must be formed either in the caseband or in the bottom, thus involving a manufacturing complication of the piece in question.
Casings are also known in the art in which the gasket of elastomeric material is cup-shaped and constitutes together with the glass a tight envelope in the proper metallic casing (CH - A - 2363/69). The latter is, however, not tight, so that water can seep into that casing and flow in the movement upon opening the casing for a repair.